Drill Holes Produced by the Predatory Gastropod Nucella Lamellosa (Muricidae): Palaeobiological and Ecological Implications

Drill holes, used widely by biologists and palaeontologists to study predator–prey interactions, provide rich quantifiable data on drilling carnivores and their victims. A laboratory experiment, involving over 50 individuals of the drilling gastropod Nucella lamellosa (Gmelin) and several hundred individuals of its natural prey, the mussel Mytilus trossulus (Gould), was employed to test the informative value and validity of several drill‐hole parameters. The majority of attacks (~88%) were accomplished by drilling, providing a record of predation intensity that is only slightly underestimated. In three out of nine cases, prey killed without drilling exhibited an incomplete drill hole, so that incomplete muricid drill holes need not record failed predatory attacks. Drill‐hole dimensions correlate with predator size, but the size and thickness of prey shell do not affect drill‐hole size. The spatial distribution of drill holes on prey shells does not suggest any obvious site‐selective stereotypy in drilling behaviour. The drill‐hole morphology is relatively invariant in terms of vertical profile, but highly variable in outline. Although none of the holes produced in the experiment could readily be mistaken for a naticid drilling, the high variability in outline could be misinterpreted (especially if data came from the fossil record) as evidence for presence of multiple types of predators.